Low flux density ferromagnetic material



May 30, 1961 J. M. BROWNLOW LOW FLUX DENSITY FERROMAGNEZTIC MATERIAL Filed May 27, 1960 AOL mmDhqmmnzzmt.

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oom wm om w com FLUX DENSITY B (GAUSS) INVENTOR JAMES M. BROWNLOW BY M 6%;

ATTORNEY United rates atent 2,986,522 LOW FLUX DENSITY FERROMAGNETIC MATERIAL James M. Brownlow, Fishkill, N.Y., assignor to Inter national Business Machines Corporation, New York, N.Y., a corporation of New York Filed May 27, 1960, Ser. No. 32,367

3 Claims. (Cl. 252-625) This invention relates to ferromagnetic materials and more particularly to Cr-Mn-Ni ferrospinel compositions exhibiting low flux densities.

Ferrospinels have been employed in the past as magnetic memory elements and as pulse transfer elements in computers and other data processing apparatus. Usually a limiting factor in the frequency of the read-write operation of the apparatus is the overheating of the materials at high repetition rates, requiring elaborate machine cooling procedures. The power dissipated during switching is proportional to the amount of flux which is being switched. Accordingly, ferrite materials which may be switched from one operating state to another with only a small amount of flux change offers a possible solution to this bottleneck.

Therefore, an object of the present invention is to provide materials having the requisite characteristics for operation as memory and pulse transfer element in computers and which in addition, exhibit low flux densities.

A particular object of the instant invention is to provide a memory ferrospinel having a low flux density and fast switching behavior during the writing operation.

The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention, as illustrated in the accompanying drawing.

In the drawing, the figure is a plot of flux output versus temperature for typical Cr-Mn-Ni ferrospinel compositions of the present invention; namely, Bodies No. T136 and T143.

The low flux density ferrospinel composition of the present invention comprises a chromium-manganesenickel ferrite in proportions as will be described hereinafter and set forth in Table I below.

TABLE I Body Number Cr Mn Ni Fe Br/Bs To B 10 z y 2 C.) (gauss) 0. 70 1. 30 0. 20 0. 80 0. 9 110 200 0. 67 1. 03 O. 16 1. 14 0. 95 198 3P0 0. 98 0. 98 0. 20 0. 84 0. 9 130 200 0. 67 0. 86 0. 17 1. 27 0. 95 220 400 1. 10 0. 70 0. 20 l. 0. 8 155 200 l. 12 0. 98 0. 20 0. 70 0. 8 80 170 0. 70 1. 50 0. 20 0. 60 0. 8 68 200 0. 42 1. 54 0. 20 0. 84 0. 8 140 330 O. 42 1. 26 O. 20 l. 12 O. 8 220 370 0. 61 1. 22 0. 15 1. 02 O. 9 180 220 0. 70 0. S0 0. 26 1.20 0. 95 200 380 0. 70 0. 90 0. 35 l. 00 0. 9 160 400 The compositions which exhibit a low flux density, fast switching characteristics, high Br/Bs ratios and low coercive forces consist of compounds of the formula:

Cr Mn Ni Fe O where (in atom numbers) w+x*I-y+z=3.

w=0.4-1.2 x=0.7-1.6 y=0.10.4

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The ferrites are prepared in the manner well known in the core art. A chromium compound, a manganese compound, a nickel compound and an iron compound is heated in air or nitrogen at temperatures between 1100- 1500 0., preferably about 1400 C. to form the desired ferrite composition.

Example A mixture consisting of finely divided powders in desired proportions of chromic oxide, manganese oxide, nickel carbonate and ferric oxide is calcined at 900 C. Thereafter the cores are pressed from these powders, sintered at a temperature of about 1400 C. for about two hours in air and preferably refired in air at a lower temperature. Preferred firing and cooling cycles for several compositions are set forth in Table II below. While the second firing cycle is preferred, useful core products from the same composition are also obtained using only one firing cycle, wherein the sintered cores are quenched or cooled slowly from the firing temperature.

TABLE II Fire I Fire II Identification No.

T ergp Time Tgnp Cooling Cycle 1, 350 16 hrs None Quenching.

350 16 hrs. quenched 1, 000 20 min. quenching. 1,400 60 min. quenched 1,000 10 min. Slow cool to 200 0. quenching. T 136 1, 400 10 min. quenched 1, 200 10 min. quenched. T 162 1,400 30min. quenched 55. 10 min. Slow cool to 20 C.

TABLE I11 Sw (High Threshold H) (0e.- Field (0e.) microsee.)

Identification N0.

The ferrite compounds are particularly advantageous in that they possess the requisite characteristics for operation as memory materials in computer circuitry, namely, square hysteresis loop, square knee, low coercive force and fast switching, and in addition, have a very low flux density, in the order of 200 gauss, which reduces the heating effect during pulse operation by a factor of 10. For example, the ferrites of the present invention may be used to advantage in the two-dimensional memory scheme described in detail in the papers by R. D. McMahon in the Proceedings of the Solid State Circuits Conference, February 12, 1959, page 16 of Digest Technical Papers and in the paper by W. L. Shevel, Jr. and O. A. Gutwin in the Proceedings of the International Solid States Circuits Conference, February 11, 1960, page 62 of Digest of Technical Papers. Using a bias current of 2 oersteds and operating at 10% margins of a 4 oersted half-select drive current, it was possible to write information into the core in millimicroseconds. Since the time cycle in this scheme is limited only by the write time, it is seen that the ferrites of the present invention are capable of very high speed operation. Furthermore, since only a small amount of flux is being switched during the operation, only normal cooling is required.

The core materials of the present invention also may be utilized to considerable advantage in other ferrite memory switching techniques, such as the two core-perbit scheme described in detail in an article by G. H.

Perry and S. J. Widdows in the Solid States Circuit' Conference, Digest of Technical Papers, page 58, February 11, 1960. Using this scheme the word line was pulsed with S oersteds and the digit line with 0.8 oersted. The write time was only 75 millimicroseconds. Operating at a repetition rate of 3 megacycles, only ambient air cooling was required. With an 11 oersted drive current on the Word line and a 2.4 oersted drive current on the digit line, the write time was reduced to 20 millimicroseconds.

A further advantage of the ferrites of the present invention is illustrated in the figure. The graph demonstrates the near linear relationship of flux output with temperature for bodies of the present invention. Therefore, for small changes in temperature during the switching operation, the magnetic characteristics of the core remain relatively constant.

While the invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention.

What is claimed is:

1. A low flux density memory ferrite produced by heating in an air atmosphere at a temperature of about 1400 C., a mixture of chromic oxide, manganese oxide,

nickel oxide and ferric oxide in proportions present in a composition having the formula Cr Mn Ni Fe 0 where w is between 0.4-1.2, x is between 0.7-l.6, y is between 0.1-0.4, z is between 0.61.3 and w+x+y+z is not greater than 3, said ferrite having a flux density, B, less than 400, a value of Br/Bs greater than 0.7, a coercive force about 2 oersteds and a switching constant of about 0.2 oersted-microsecond. Y

2. A low flux density ferromagnetic composition produced by heating in an air atmosphere at a temperature of about 1400 C., a mixture of chromic oxide, manganese oxide, nickel oxide and ferric oxide in proportions present in a composition having the formula Cr Mn Ni Fe O where w is 0.60.7, x is 0.9-1.3, y is 0.1-0.2, z is 0.81.2 and w+x+y+z is not greater than 3, said ferrite having a flux density, B, less than 400, a value of Br/Bs greater than 0.7, a coercive force of about 2 oersteds and a switching constant of about 0.2 oersted-microsecond.

3. The ferrite according to claim 2 where w=0.67, x:1.03, y=0.16 and z=1.l4.

References Cited in the file of this patent UNITED STATES PATENTS 

1. A LOW FLUX DENSITY MEMORY FERRITE PRODUCED BY HEATING IN AN AIR ATMOSPHERE AT A TEMPERATURE OF ABOUT 1400*C., A MIXTURE OF CHROMIC OXIDE, MANGANESE OXIDE, NICKEL OXIDE AND FERRIC OXIDE IN PROPORTIONS PRESENT IN A COMPOSITION HAVING THE FORMULA CRWMNXNIYFEZO4 WHERE W IS BETWEEN 0.4-1.2, X IS BETWEEN 0.7-1.6 Y IS BETWEEN 0.1-0.4, Z IS BETWEEN 0.6-1.3 AND W+X+Y+Z IS NOT GREATER THAN 3, SAID FERRITE HAVING A FLUX DENSITY B, LESS THAN 400, A VALUE OF BR/BS GREATER THAN 0.7, A COERCIVE FORCE ABOUT 2 OERSTEDS AND A SWITCHING CONSTANT OF ABOUT 0.2 OERSTED-MICROSECOND. 